This invention relates to a body support system such as may be used for a seat cushion. More particularly, this invention relates to a body support system such as may be used for a seat cushion and having improved mechanical response characteristics and improved thermal interaction with a user.
The comfort provided to a user by a body support system such as a seat cushion will depend on a variety of factors. One such factor is the mechanical response of the body support system to the compressive and shear forces applied by a user interfacing the body support system, e.g., a user seated on a cushion. Mechanical response includes static and dynamic responses. Another such factor is the ability of the body support system to provide thermal regulation with a user resulting from the inherent heat exchange process/mechanisms in the body support system. If the body support system is to be used in conjunction with a moving vehicle/vessel/device including a wheelchair, a farm implement such as a tractor or riding mower, or as a seating element for public transportation, then the ability of the body support system to provide adequate dynamic response characteristics to applied dynamic excitations and reduce Whole Body Vibration (WBV) by means of reducing transmission of harmful frequency components to the user, is another factor.
Conventional contemporary office seats are usually made of either upholstered padding or synthetic mesh in a frame assembly. Each of these types of seats has its own characteristic thermal properties. Padded upholstery (e.g., polyurethane foam) seating provides limited heat exchange with the user, which however mainly occurs through conduction and sweat evaporation processes. As a result, upholstered padding is better suited for lower workspace temperatures on the order of 16-25xc2x0 C. (61-77xc2x0 F.) and shorter sitting times before heat starts to build up and un-evaporated sweat starts to develop at the user-body support system interface On the other hand, mesh seating provides excessive heat exchange between the surrounding environment and the user mainly through radiation and convection heat exchange processes. In the case of mesh seating, these heat exchange processes do not depend on intrinsic properties of the body support system, but also depend on extrinsic factors such as surrounding environmental parameters including temperature and air speed, and on factors such as workspace configuration, surface orientations, and temperatures and thermal reflectivity of adjacent surfaces such as floor and walls. As a result, mesh chairs may be better suited for higher workspace temperatures of 25-35xc2x0 C. (77-95xc2x0 F. and longer sitting times. Neither of these prior art seating designs provides for thermal regulation in a wide variety of office temperature environments and workspace configurations.
Another disadvantage of mesh seat upholstery is its tendency to xe2x80x9ccreep,xe2x80x9d that is, to deform viscously or irrecoverably, with disproportional stress-strain rate characteristics especially in the territrial stress-strain regime, which might be reached (for many mesh materials)when the user""s weight is large, therefore resulting in non-uniform mechanical response to a wide range of users. Creep is a significant problem when the seat mesh is subjected to heavy sustained user""s weight over prolonged time. Control of creep usually requires cross directional mesh reinforcement with fibers that have very limited creep characteristics. Without proper control, however, creep can cause excessive deformation in the seat mesh, eventually leading to loss of contact at the user-seat interface, and a severe reduction in the total load carrying capacity of the body support system. This results in excessive cognitive (conscious and sub-conscious) weight shifting towards the front under-thighs and to the feet- and armrests, factors that may be directly related to discomfort and unfavorable ergonomic conditions.
Thermal properties are major ergonomic features that should be considered in the design of an office chair. The human body always works to retain its core temperature near 37xc2x0 C. (98.6xc2x0 F.), by means such as postural adjustments, varying skin temperatures such as by perspiration, regulation of cardiovascular and pulmonary activity such as pulse and breath rates to affect blood flow and vessel sizes especially in skin areas close to a heat-exchanging interface such as that with a seat cushion. A chair that prompts sweating after a relatively short period of sitting and which requires the human body to engage in such thermal self-regulatory processes will be uncomfortable and may affect work efficiency/productivity. For example, with conventional upholstered padding, heat can quickly build up at the user/seat interface causing the user to limit metabolic rates such as muscular activity to reduce heat generation, therefore severely affecting work efficiency. The user may also begin sweating to initially expedite the thermal transfer across the user skin, and to attempt to prompt the sweat evaporation cooling process. When the user/seat interface inhibits sweat evaporation due to low cushion vapor permeability under even small pressures, heat is not dissipated at the interface leading to even greater discomfort for the user. On the other hand, mesh chairs have high vapor permeability and heat dissipation and do not allow for any heat build up at the seat user interface. With colder workspace environments, and closer, oppositely oriented, highly reflective, and cold office space surfaces (floors/walls, etc.), and with high (transient or steady) airspeeds, the user is set to become responsible to generate heat that seeks thermal equilibrium with the whole environment; a condition that prompts discomfort. This might allow for excessive user heat loss or gain. It is therefore postulated that a limited heat build up at the interface would be favorable to reverse the thermal gradient across the interface. Thus, with open mesh seats the thermal comfort of the user becomes significantly dependent on the ambient temperature of the work environment and configuration.
Further, conventional seating designs do not provide for variations in the size and comfort levels of different users. Different individuals will have different load characteristics and different thermal generation rates therefore producing different comfort levels (including psychometrics).
It is thus one object of the invention to provide a body support system such as a seat cushion having improved thermal regulation properties.
It is yet another object of the invention to provide a body support system such as a seat cushion having improved mechanical response properties including wider low intensity pressure distribution and better dynamic response characteristics.
It is also another object of the invention to provide a an energy dissipation system as a component of the body of the support system to provide even greater comfort to a user.
It is still another object of the invention to provide a body support system such as a seat cushion in which the thermal regulation properties and/or the mechanical characteristics can be varied to the needs or preferences of a particular user or group of users by varying amongst the many design parameters in the system.
A body support system is provided having improved mechanical (static and dynamic) support characteristics and improved thermal interaction with a user. The improved static support is provided by means for distributing the weight of a user in response to applied compressive and shear forces at the user-support system interface. The means for distributing the weight of the user comprises a plurality of vertical columns disposed substantially centrally in said body support system. Without connecting the columns by means of an elastomeric layer, the columns are capable of deflecting substantially independently of one another in response to the compressive forces applied by a user. The improved thermal interaction is provided by structures that provide enhanced airflow through and about said body support system, thereby providing for convective thermal regulation, and dry and evaporative heat exchange. An elastomeric member disposed above said columns also serves to facilitate heat exchange with a user, and cooperates with the columns in the distribution of the user""s weight for improved static and dynamic support. The elastomeric layer acts to level out column deflections, therefore limiting the reaction acting back on the user by an individual column and invoking a more collective response, therefore reducing interfacial pressure peaks and gradients. The improved dynamic response is achieved by dampening the peak amplitudes of the response and filtering out harmful frequency components of the dynamic loading. Proportioning the mass and stiffness substantially determines the desirable dynamic response properties of the body support system.
The body support system comprises a foam body. In one embodiment, the vertical columns can be configured as upwardly extending risers, formed integrally with said foam body. In an alternative embodiment, the columns can extend downwardly from the elastomeric member. The columns can be formed of a material having density and mechanical response characteristics either the same as or different from the density and mechanical response characteristics of the foam body. This feature permits the inventive body support system to be customized to the needs of different users.
The spaces between the vertical columns define a reservoir for a fluid such as air within the interior of the body support system. The body support system further comprises means for displacing and/or directing the flow of fluid, typically air, from the fluid (air)reservoir to the periphery of the body support system, and then toward the upper surface thereof, for heat exchange processes with the user, thereby increasing the comfort of the user when using the body support system for long periods of time. The means for directing the flow of fluid from the fluid reservoir to the periphery can comprise a plurality of channels formed within the foam body and extending from the air reservoir to the foam body periphery. When compressive forces are applied by a user, fluid (air) within the reservoir will be displaced and directed through the channels toward the periphery and upwards. Advantageously, airflow through the body support system is achieved without the need for active airflow circulation devices such as fans, blowers, valves, or pumping devices. Air deflecting means disposed about the periphery of the foam body function to deflect the air received at the periphery from the reservoir to a region above the foam body for heat exchange with the user. This thermal regulation function is further enhanced by the aforementioned elastomeric member, which functions as a large capacity heat sink to remove heat from a user generating excessive heat
The body support system of the instant invention can further comprise an air-permeable viscoelastic layer disposed above the elastomeric member and the foam body. The viscoelastic layer can reduce the transmission of both compressive and shear forces to the elastomeric member. The air-permeable viscoelastic layer can also facilitate the flow of displaced air at the periphery of the cushion to enhance thermal regulation. The airflow achieved with the body support system of the instant invention also contributes to mechanical function of the body support system by providing recoverable dissipation of applied shear and compressive forces
The body support system of the instant invention can further comprise energy modulation means for converting the vertical component of the applied loading energy, such as a user""s weight, to non-vertical, such as horizontal, dissipative components, which would effectively decrease the real vertical reaction experienced by a user, therefore enhancing comfort. In one embodiment, the energy modulation means can comprise a member having a top layer and a bottom layer, each made of a flexible fluid-tight membrane, the top and bottom layers being joined at their respective peripheries to form a bladder, or flexible fluid compartment, having an interior volume, and one or more walls in said interior volume, said walls extending between the inner surface of said top and bottom layers to define a plurality of interconnected flexible fluid chambers within said interior volume, said chambers being interconnected via baffles, spaces, or minute orifices between and in said walls. Said interior volume contains a viscous fluid that can flow in and among the various interconnected chambers. When a force such as the weight of a user is applied to the top of the energy modulation means, at least some of the viscous fluid in those chambers directly beneath the force is further pressurized and squeezed out from chambers experiencing higher pressurization due to vertical force application to other chambers experiencing less of such force. The horizontal movement of the viscous fluid between the interconnected chambers dissipates the energy applied by the user so that the user experiences less resistance and greater comfort. The energy dissipation means presents many parameters that can be varied to meet the needs of a particular user or a particular type of use. These parameters include, for example, the materials used in the top and bottom layers and interior walls, the dimensions of the layers and walls, the dimensions of the spaces or orifices interconnecting said chambers, and the volume and viscosity of the viscous fluid. In an alternate embodiment, the flexible fluid compartments may be all fully connected to form a full one fluid compartment, filled with viscous fluid that may optionally be pressurized. In another embodiment, such full compartment may be depressurized and evacuated from fluid, so that it can fill with air or fluid pouring into it from an outside source by means of an inlet flexible tube, equipped with a one-way valve, therefore, providing means to store such externally pouring fluid, and means to later dispose of it, by means of an outlet flexible tube, equipped with a one-way valve, by either using differential static pressure or by using of micro-pumps attached to such pressurized or un-pressurized fluid containment system. In at least one of the embodiments above, the flexible fluid compartment may be inflated with air of fluid from an external source in order to provide a back reaction on the underside of the said elastomeric layer. Such back reaction would transmit back to the user through the optional overlay, thereby providing means to stiffen the body support system when needed
The body support system of the instant invention can be used in a wide variety of seating applications. The body support system can be configured as a seat cushion such as for use in office seating, in which case the seat cushion can be mounted onto a chair frame including a preformed seat pan. The seat pan acts as a high-stiffness or as a rigid support for the cushion. The body support system can also be used in rehabilitative seating and other body support applications, such as in wheelchairs, hospital beds, sports cushions, such as in stadiums, and the like, where improved responsiveness to compressive and shear forces can help in the prevention of pressure concentrations which might lead to decubitus ulcers. It can also be used in seating or bedding for personal assistance purposes such as the case with users confined to their seats or beds for prolonged periods of time, and requiring readily available fluid containment and management system fully embedded within the thinness of the body support system. The inventive body support system can also be used in dynamic situations such as motor vehicles, particularly vehicles driven for long periods of time such as trucks, and even more particularly vehicles driven for long periods of time over uneven surfaces, such as snowplows and farm implements, which vehicles are subject to motion-induced vibration and in which the vehicle driver can benefit from the damping of such motion-induced vibration as can be provided by the inventive body support system disclosed herein.